1. Field of the Invention
The present invention relates to a valve controller for controlling valve opening of a motor-driven valve, particularly to a controller for valve opening control when an abnormality occurs in a temperature sensor, a pressure sensor and the like. In addition, the present invention relates to a valve controller and a valve controlling method, particularly to a controller and so on for controlling valve opening of a motor-driven valve and others for adjusting flow rate of a refrigerant. Further, the present invention relates to a refrigeration and cold storage system used for a refrigeration and cold storage show case and so on, and a device and a method for controlling the system, particularly to a refrigeration and cold storage system and the like in which operation/stoppage of a compressor is switched in accordance with a temperature of a controlled object.
2. Description of the Related Art
Conventionally, in a refrigeration cycle used for refrigeration and cold storage show cases and the others, in order to accurately adjust flow rate of a circulating refrigerant, as an expansion valve for flow control, a motor-driven valve with a pulse motor for moving a valve body has widely been utilized. In this refrigeration cycle, generally, a degree of superheat is calculated after detecting inlet and outlet temperatures of an evaporator with temperature sensors, and valve opening of the motor-driven valve is controlled by comparing the calculated degree of superheat with a preliminarily set degree of superheat.
As described above, although the valve opening control of the motor-driven valve is performed based on the temperature detected by the temperature sensor, at the operation of the refrigeration cycle, there is a possibility that the temperature cannot appropriately be detected when an abnormality occurs in the temperature sensor due to disconnection, short circuit and the like in operation, in such case, it becomes impossible to continue the valve opening control of the motor-driven valve also. Then, in a conventional valve controller, in its manufacturing stage, a fully-closed value or a fully-opened value is set as an opening value for emergency, when an abnormality occurs in the temperature sensor, the motor-driven valve is controlled to stop in the fully-closed or fully-opened state (see Patent document 1 as an example).
But, when the motor-driven valve is stopped in the fully-closed state, after that, all the while, a refrigerant does not flow in the refrigeration cycle, so that the operation of the refrigeration cycle stops due to a low-pressure abnormality, which makes it impossible, as an example, to maintain inside temperature of a refrigeration and cold storage show case low. As a result, until a maintenance worker arrives, the inside temperature remains high over a long period of time, resulting in bruised foods.
On the other hand, in case that the motor-driven valve is stopped in the fully-opened state, circulation of the refrigerant is not stopped but the quantity of refrigerant fed to the evaporator becomes too much, so that a refrigerant from the evaporator is returned to the compressor in the form of liquid (liquid back). In this case also, the show case cannot be cooled in the same manner as described above, which may cause bruised foods, moreover, there is a fear that the compressor is damaged through liquid compression.
These problems can be generated not only when an abnormality occurs in the temperature sensor but in a pressure sensor for detecting pressure of a refrigerant circulating in the refrigeration cycle almost in the same manner as described above, so that it has been a key problem to consider a measure in case of abnormality in the sensors for detecting temperature and pressure in the refrigeration cycle.
Further, conventionally, in refrigeration cycle systems used for air-conditioners, refrigeration and cold storage show cases, and the like, flow rate of a circulating refrigerant is adjusted for the purposes of stabilizing a cooling capacity, efficient operation, and the like, and in order to accurately performing the adjustment, as an expansion valve for controlling the flow rate, a motor-driven valve that is a motor-driven expansion valve with a pulse motor for moving the valve body has been widely utilized.
However, since the valve opening control of the motor-driven valve is generally performed with an open-loop control that doesn't feed back an absolute opening (actual opening), in addition, when a power-supply to the motor-driven valve is stopped, the valve body in the motor-driven valve stops at a position when the power-supply is stopped without returning to an initial position, so that at and after the second a power-supply after the first supply, it is impossible to exactly grasp an absolute opening (a position of the valve body) when the power-supply is started.
Therefore, in the control of the motor-driven valve, generally, an initialization processing is performed when power is supplied to the valve, and the valve opening control is started after determining the initial position of the valve body (for instance, see Patent document 2). Here, it is the initialization processing to drive the motor-driven valve so as to be closed by applying the number of pulses over all the strokes from the fully-opened state to the fully-closed state to forcibly change the valve opening of the motor-driven valve to that in fully-closed state.
However, in the refrigeration cycle system, there is a possibility that foreign substances such as impure substances are generated in a refrigerant flow passage, in the foreign substances, large ones can be removed by a strainer and so on, but small ones may pass through the strainer and flow into the inside of the motor-driven valve. In such a case, in the motor-driven valve are caught the foreign substances, which may cause a shift in the valve opening of the valve.
That is, in case that the catching of the foreign substance occurs, since the foreign substance prevents the valve body from moving, for example, when a driving signal of 100 pulses are added to the pulse motor, an actual amount to be driven becomes smaller than that when driving the signal of 100 pulses are given. As a result, a difference of several pulses is generated between a valve opening estimated from the number of pulses added to the motor-driven valve and an actual valve opening of the motor-driven valve itself, after that, the motor-driven valve is operated with the valve opening including the difference.
For this reason, it becomes impossible to accurately control the valve opening of the motor-driven valve, for instance, when a driving signal for obtaining the fully-closed state is added to the motor-driven valve, the motor-driven valve is actually in a slightly-opened state. In this case, it is possible to generate a leak of a refrigerant and the like, resulting in deteriorated reliability of the device and so on.
Further, generally, in the refrigeration and cold storage show cases utilized for cold reserving and displaying foods and the like, operation/stoppage of the compressor is switched in accordance with high/low of the inside temperature, and the switching action is repeated according to the change in the inside temperature, which controls the inside temperature to be maintained constant.
The switching of the operation/stoppage of the compressor is performed in such a manner that the compressor is operated at the moment that the inside temperature becomes higher or equal to a predetermined setting temperature for turning the compressor on, and the operation of the compressor is stopped at the moment that the inside temperature becomes lower or equal to a predetermined setting temperature for turning the compressor off. A difference between the setting temperatures for turning the compressor on/off is called “DIFFERENTIAL”, which is set to avoid frequent operation/stoppage actions (hunting) of the compressor.
In addition, flow rate of a circulating refrigerant in the refrigeration cycle is adjusted for the purposes of stabilization of a cooling capacity when cooling inside of a refrigeration and cold storage showcase, efficient operation, and the like, and in order to accurately performed the adjustment, as a flow control valve for the refrigerant, a motor-driven expansion valve with a pulse motor or the like has widely been used. In the refrigeration cycle with the motor-driven expansion valve, a degree of superheat of a refrigerant flowing the evaporator is detected, and the detected degree of superheat is compared with a setting degree of superheat, and in accordance with the difference, the flow rate of the refrigerant is controlled through adjustment of the valve opening of the motor-driven expansion valve using a PID control and others.
By the way, as described above, when operation/stoppage of the compressor is switched, according to this motion of the compressor, opening/closing of the expansion valve needs to be controlled. As a method of controlling the valve, for example, in the Patent document 3 is disclosed a technique that at the stoppage of the compressor is controlled the motor-driven expansion valve so as to be fully-closed once, and a predetermined period of time later, the valve is fully-opened to uniform gas pressure in a refrigeration cycle, and when starting the operation of the compressor, the valve opening of the valve is set to be an initial opening (preliminarily set standard opening) or a memorized opening (the valve opening just before the compressor stops).
The technique disclosed in the Patent document 3 is applied to air conditioners for adjusting room temperature, so that the gas pressure in the cycle is uniformed in the fully-opened state, on the contrary, in refrigeration and cold storage show cases, to avoid increasing the inside temperature, the uniformity of the gas pressure at the stoppage of the compressor is not carried out in general. For this reason, in case that the technique described above is applied to the control of the refrigeration and cold storage show cases, when the compressor is stopped, the valve opening of the motor-driven expansion valve is controlled to be the fully-closed state, and the valve opening is set to be the initial opening or the memorized opening when starting the operation of the compressor.
However, as described above, in case that the valve opening of the motor-driven expansion valve is switched between the fully-closed opening and the initial opening (or the memorized opening) in accordance with the operation/stoppage of the compressor, in each switching operation/stoppage of the compressor, the valve opening of the valve is to be changed with great operation amount.
In addition, in the refrigeration and cold storage show cases, the number of switching of the operation/stoppage of the compressor is comparatively large, there are quite a few case that is required a heavy switching action repeating operation/stoppage at five minute intervals. In such a case, the number of switching operation/stoppage of the compressor is more than ten times an hour, resulting in seriously increased driving frequency of the motor-driven expansion valve.
Further, the motor-driven expansion valve is a machine component with sliding parts, so that as the driving frequency increases, abrasion of the sliding parts advances to shorten the life of the valve, and its durability life is generally defined in terms of the number of the driving pulses added to the pulse motor. For this reason, when the number of driving pulses added to the pulse motor is considerably increased by changing the valve opening as described above, remaining number of pulses defined as the durability life are rapidly consumed, resulting in shortened life of the motor-driven expansion valve. As a result, frequent replacements of the motor-driven expansion valve are forced to be carried out, consequently, generating a problem of decreased reliability of the refrigeration and cold storage show cases.
Patent document 1: Japanese Patent Publication No. Heisei 11-230624 gazette
Patent document 2: Japanese Patent No. 3936345 gazette
Patent document 3: Japanese Examined Utility Model Publication (Kokoku) No. Heisei 2-3093 gazette